The present invention relates generally to dunnage bags and is particularly directed to dunnage bags of the type which require no separate bladder. The invention is specifically disclosed as a bladderless dunnage bag made of a coated extensible paper substrate material which exhibits properties of being extrudable, impermeable to air, heat sealable, and able to absorb shock energy.
FIG. 1 shows a conventional dunnage bag that is constructed of a paper layer as the outer portions and a plastic layer as the inner portions, in which the inner portions or layer is also termed a xe2x80x9cbladder.xe2x80x9d This prior art dunnage bag, generally designated by the reference numeral 10, has been in use for years, and all such paper dunnage bags include the plastic bladder on the interior portions due to the porosity of paper. The plastic bladder is designated at the reference numeral 12, and in many conventional dunnage bags is constructed of polyethylene. In FIG. 1, the two outer layers 14 are each constructed of paper.
The bottom portions (as viewed on FIG. 1) of the conventional dunnage bag 10 are made into a seal, which is generally designated at the reference numeral 20. This seal 20 is typically made to be both air-tight and also watertight in situations where the atmosphere is typically humid, or if the internal air spaces are typically humid. In addition, if the dunnage bag 10 were to be filled with some type of liquid instead of a gas (this would be unusual), then the bladder 12 would also have to be liquid-tight for that particular type of liquid.
Since the seal 20 is typically made by use of an adhesive and by folding the outer paper layer 16 over upon itself, the strength of the paper material used for the outer paper layer 16 is the limiting factor for the strength of this seal at 20. Since the bonding to make the seal is typically paper-to-paper sandwiching glue or other adhesive, the strength of the paper is the limiting factor as noted above, and for many conventional dunnage bags the internal pressure is thereby limited to perhaps 2-3 PSI above atmospheric pressure. If the internal pressure becomes too large, the pressure will cause the paper to fail before the glue itself would fail. While additional layers of paper could be used to increase the dunnage bag""s burst rating, it will nevertheless be true that the strength of the paper-to-paper bonding will be the limiting factor of the internal pressure rating of the conventional bag.
As will be understood by those skilled in the art, the conventional dunnage bag illustrated in FIG. 1 represents only a portion of a full dunnage bag that will have seals or paper folds along all of its outer end surfaces. The partial cut-away view of FIG. 1 is illustrative of the construction of such dunnage bags using various layers of materials.
Accordingly, it is a primary advantage of the present invention to provide a dunnage material capable of forming a bladderless dunnage bag to restrain shipping loads in vehicles, railroad cars, and ships, in which the dunnage material is formed of a paper substrate with a resin coating on at least one of its surfaces.
It is another advantage of the present invention to provide a bladderless dunnage bag having center seals and end seals that are stronger than the paper material that creates the substrate of the dunnage material forming the bag.
It is a further advantage of the present invention to provide an extrudable resin material that can be used as a coating on extensible kraft paper, which can absorb shock energy, is impermeable to air, and is heat sealable, and further after being applied to the kraft paper, will improve the paper""s bursting strength, puncture resistance, tear resistance, tensile strength, wet strength properties, and energy absorption properties.
It is yet another advantage of the present invention to provide a method for manufacturing dunnage bags by coating an extensible paper with a resin material on one or both surfaces of the paper, which allows for the formation of a bladderless dunnage bag, and to provide a method in which the coating is applied by an extrusion process, and further to create center seals and end seals that can be heat sealable while the material is in motion.
Additional advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.
To achieve the foregoing and other advantages, and in accordance with one aspect of the present invention, an improved material used to construct bags is provided, the material comprising a flexible paper substrate, the paper substrate having a first surface and a second surface; a first coating material substantially covering the entire first surface of the paper substrate, the first coating material comprising a compound consisting of a low density polyethylene and a metalacene process polyethylene; and a second coating material substantially covering the entire second surface of the paper substrate, the second coating material comprising a compound consisting of a low density polyethylene and a metalacene process polyethylene.
In accordance with another aspect of the present invention, a material used to construct bags is provided, comprising a flexible paper substrate, the paper substrate having a first surface and a second surface; and a coating material substantially covering the entire first surface of the paper substrate, the coating material comprising a compound consisting of a low density polyethylene and a metalacene process polyethylene.
In accordance with yet another aspect of the present invention, a bladderless dunnage bag is provided, comprising a flexible sheet material having a substrate with a coating on at least one surface of the substrate, the substrate comprising an extensible material, the coating comprising a material that is impermeable to air, heat sealable, and able to absorb shock energy; and the flexible sheet material being formed into a dunnage bag shape by use of at least one seal along a longitudinal axis of the dunnage bag, and at least one seal along a transverse axis which is substantially perpendicular to the longitudinal axis; in which the coating forms an inner surface of the dunnage bag.
In accordance with a further aspect of the present invention, a method for constructing a bladderless dunnage bag is provided, comprising (1) providing a flexible sheet material having a substrate with a coating on at least one surface of the substrate, the substrate comprising an extensible material, the coating comprising a material that is (a) impermeable to air, (b) heat sealable, and (c) able to absorb shock energy; (2) folding the flexible sheet material over upon itself to begin its shaping into a dunnage bag form; (3) forming at least one seal along a longitudinal axis of the dunnage bag form; and (4) forming at least one seal along a transverse axis which is substantially perpendicular to the longitudinal axis; and in which the coating forms an inner surface of the dunnage bag.
In accordance with still a further aspect of the present invention, a method of manufacturing a bladderless dunnage bag is provided, comprising (1) roll rewinding of a flexible sheet material having a substrate with a coating on at least one surface of the substrate, the substrate comprising an extensible material, the coating comprising a material that is impermeable to air, heat sealable, and able to absorb shock energy; (2) folding the flexible sheet material over upon itself to begin its shaping into a dunnage bag form, and forming a center seal; (3) forming the flexible sheet material into a spaced-apart configuration using a tube forming station; (4) punching a hole in the flexible sheet material and installing and sealing thereto an air inlet valve; (5) slitting side edges proximal to an open end of the dunnage bag form; (6) creasing and folding the first sheet portion along a crease line between the slit side edges; (7) sealing the folded first sheet portion to create an inner end seal; (8) double creasing and double folding both the first and second sheet portions onto themselves along a line proximal to the inner end seal; and (9) sealing both the folded first and second sheet portions to create an outer seal at sufficient locations of the flexible sheet material to achieve an air-tight dunnage bag.
In accordance with yet a further aspect of the present invention, a method of manufacturing dunnage material for use in a bladderless dunnage bag is provided, comprising (1) combining a low density polyethylene material with a metalacene process polyethylene to create a coating resin that is extrudable; (2) providing a roll of uncoated extensible paper, and unwinding that roll such that the extensible paper forms a web that passes an inner coating station and an outer coating station; (3) at the inner and outer coating stations, applying the coating resin to both surfaces of the paper web using an extrusion process; and (4) winding the coated paper web onto a second roll.
In accordance with still another aspect of the present invention, a method of manufacturing a bladderless dunnage bag is provided, comprising (1) combining a low density polyethylene material with a metalacene process polyethylene to create a coating resin that is extrudable; (2) providing a roll of uncoated extensible paper, and unwinding that roll such that the extensible paper forms a web that passes an inner coating station and an outer coating station; (3) at the inner and outer coating stations, applying the coating resin to both surfaces of the paper web using an extrusion process; (4) winding the coated paper web onto a second roll; (5) unwinding the coated paper web from the second roll and directing it to a center seal station where the flexible sheet material is folded over upon itself to form a center seal and to begin its shaping into a dunnage bag form; (6) forming the flexible sheet material into a spaced-apart configuration using a tube forming station; and (7) forming at least one end seal by use of a creasing and folding operation.
Still other advantages of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.